1. Field of the Invention
The invention relates to crosslinked polyphenylene ether resins and more specifically, relates to the manufacture of three-dimensional copolymers of polyphenylene ether resins and styrenic resins.
2. Brief Description of the Related Art
Polyphenylene ether (PPE) resins (also known within the art as xe2x80x9cPolyphenylene Oxidexe2x80x9d) are an extremely useful class of high performance engineering thermoplastics by reason of their hydrolytic stability, high dimensional stability, toughness, heat resistance and dielectric properties. PPE resins are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. This unique combination of properties renders PPE based formulations suitable for a broad range of applications which are well known in the art. One example is injection molded articles which are used for high heat applications. The more common PPE resins known in the art typically comprise polymers of a fairly high molecular weight for combination in the melt phase with other polymers. The PPE polymers of the more common PPE resins generally have in excess of 50 repeat monomer units, most often in excess of 80 or more repeat monomer units and intrinsic viscosity greater than 0.20 dl/g measured at 25xc2x0 C. in chloroform.
Styrenic resins, such as styrene-acrylonitrile resins (SAN resins) are typically transparent resins used in a variety of products including housewares, packaging, appliances, industrial batteries, and automotive and medical applications. Styrenic resins are typically used in these markets because of their low unit cost and clarity. SAN resins are typically used for their heat resistance, good processability and resistance to chemicals.
The present invention provides a composition comprising a cross-linked copolymer having PPE resin segments and segments of one or more styrene units, acrylonitrile units and combinations of styrene and acrylonitrile units. The PPE segments are derived from a PPE resin having an intrinsic viscosity of 0.20 dl/g or less as measured in chloroform at 25xc2x0 C. This PPE resin comprises PPE polymer chains having at least one end cap containing at least one pair of unsaturated aliphatic carbon atoms, i.e. carbon-carbon double bonds.
The present invention also provides a method for making a cross-linked copolymer composition. This method comprises introducing a PPE resin into a reaction medium comprising styrenic monomers and acrylonitrile monomers, wherein the amount of PPE resin loaded is 20 wt % or more of the combined total of PPE resin, plus styrenic monomers and acrylonitrile monomers. The PPE resin comprises at least one PPE polymer chain having at least one end cap comprising unsaturated aliphatic carbon atoms. The PPE resin, styrenic monomers and acrylonitrile monomers introduced into the reaction medium are polymerized. The reaction medium can be a bulk reaction medium or a medium that contains another liquid that suspends or emulsifies the reaction components.
It has been discovered that three-dimensional copolymers of polyphenylene ether resins and styrenic resins can be formed by using end-capped PPE polymers having an intrinsic viscosity of 0.20 dl/g or less measured at 25xc2x0 C. in chloroform.
A PPE resin comprising PPE polymer chains is employed to provide PPE segments for the crosslinked copolymer. These PPE polymers arm known polymers comprising a plurality of phenylene ether units of the formula (I): 
Each structural unit may be the same or different, and in each structural unit, each Q1 is independently a halogen, primary or secondary lower alkyl (i.e., alkyl containing up to 7 carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy, at least two carbon atoms separate the halogen and oxygen atoms; and each Q2 is independently a hydrogen, halogen, primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined for Q1. Most often, each Q1 is alkyl or phenyl, especially C1-4 alky, and each Q2 is hydrogen or alkyl (C1-4 alkyl).
Specific polyphenylene ether polymers useful in the present invention include but are not limited to
poly(2,6-dimethyl-1,4-phenyleneether);
poly (2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether);
poly(2,3,6-trimethyl-1,4-phenylene ether);
poly(2,6-diethyl-1,4-phenylene ether);
poly(2-methyl-6-propyl-1,4-phenylene ether);
poly(2,6-dipropyl-1,4-phenylene ether);
poly(2-ethyl-6-propyl-1,4-phenylene ether);
poly(2,6-dilauryl-1,4-phenylene ether);
poly(2,6-diphenyl-1,4-phenylene ether);
poly(2,6-dimethoxy-1,4 phenylene ether);
poly(2,6-diethoxy-1,4-phenylene ether);
poly(2-methoxy-6-ethoxy-1,4-phenylene ether);
poly(2-ethyl-6-stearyloxy-1,4-phenylene ether);
poly(2,6-dichloro-1,4-phenylene ether);
poly(2-methyl-6-phenyl-1,4-phenylene ether);
poly(2-ethoxy-1,4-phenylene ether);
poly(2-chloro-1,4-phenylene ether);
poly(2,6-dibromo-1,4-phenylene ether);
poly(3-bromo-2,6-dimethyl-1,4-phenylene ether); or mixtures thereof.
Suitable PPE resins include homopolymers and copolymers of the structural units of formula I. The preferred homopolymers are those containing 2,6-dimethyl-1,4-phenylene ether units. Suitable copolymers include random and blocked copolymers containing such units in combination with, for example, 2,3,6-trimethyl-1,4-phenylene ether units to produce poly (2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether) resins. Also included are PPE resins containing moieties prepared by grafting vinyl monomers or polymers such as polystyrenes and elastomers, as well as coupled PPE resins in which coupling agents such as low molecular weight polycarbonates, quinones, heterocycles and formals undergo reaction in a known manner with the hydroxy groups of two poly(phenylene ether) polymer chains to produce a higher molecular weight polymer, provided a substantial proportion of free hydroxyl groups remains.
The term xe2x80x9cpolyphenylene ether resin,xe2x80x9d (and xe2x80x9cPPE resinsxe2x80x9d) as used in the specification and claims herein, includes unsubstituted polyphenylene ether polymers, substituted polyphenylene ether polymers wherein the aromatic ring is substituted, polyphenylene ether copolymers and blends thereof.
The PPE resins contemplated for use in the present invention include all those presently known, irrespective of variations in structural units or ancillary chemical features which have an intrinsic viscosity (I.V.) of 0.20 dl/g or less as measured in chloroform at 25xc2x0 C. by the methods described below.
Verify bath temperature is at 25xc2x0 C.xc2x10.1xc2x0 C.
All I.V. measurement should be done on PPE resin that has been dried in a vacuum oven for a period of at least 1 hour at a temperature of 125xc2x0 C. The dried PPE resin should be allowed to cool for about 5 minutes prior to weighing.
Using an analytical balance, place a 2 oz bottle (with cap) on balance and tare. Weigh film in the bottle, target about 0.4000 grams. Record powder weight on sample long sheet.
Tare the weight of bottle (with cap) and powder. Add 50 ml of chloroform. Record weight of the chloroform on the sample log sheet. Place bottle on shaker, shake sample until it is dissolved.
To run a sample, add about 24 ml of filtered sample (filter through 12 ml autovial filters) into viscometer. Remove filter from inlet port of viscometer. Attach squeeze bulb to vacuum line on the viscometer. Slowly draw sample up the viscometer until it is 0.6 cm above the upper measurement line. Remove the squeeze bulb and vent stopper from the viscometer. As the sample reaches the upper measurement line, begin timing of the drop using a timer. When the sample reaches the lower measurement line, stop timing.
Record drop time of sample on sample log sheet.
The I.V. can be calculated using software known in the art for such calculations.
The intrinsic viscosity of the PPE resin used to form the crosslinked copolymer of the present invention is typically in the range of about 0.08-0.20 dl/g, as measured in chloroform at 25xc2x0 C.
The PPE resin herein are generally obtained by oxidative coupling at least one monovalent phenol species, preferably at least a portion of which have substitution in at least the two ortho positions and hydrogen or halogen in the para position, using an oxygen containing gas and a complex metal-amine catalyst, preferably a copper (I)-amine catalyst, as the oxidizing agent and, preferably extracting at least a portion of the metal catalyst as a metal-organic acid salt with an aqueous containing solution.
In general, the molecular weight of the polyphenylene ether resins can be controlled by controlling the reaction time, the reaction temperature and the amount of catalyst. Longer reaction times typically provide a higher average number of repeating units and a higher intrinsic viscosity. At some point, the desired molecular weight (intrinsic viscosity) is obtained and the reaction terminated by conventional means. For example, in the case of reaction systems which make use of a complex metal catalysts, the polymerization reaction may be terminated by adding an acid, e.g., hydrochloric acid, sulfuric acid and the like or a base e.g., potassium hydroxide and the like or the product may be separated from the catalyst by filtration, precipitation or other suitable means as taught by Hay in U.S. Pat. No. 3,306,875.
When combining PPE resins with other resins by either blending, curing or copolymerization reactions, including free radical reactions, it is highly desirable from the standpoints of low viscosity for mixing and a high endgroup number for functionalization to employ a PPE polymer with less than 50 repeat monomer units on average, and preferably less than about 35 repeat monomer units on average.
Recent advances in PPE resin process chemistry have allowed for the development of a low molecular weight PPE resin, an example of which is known as PPO12, which is ideally suited for forming the crosslinked copolymers of this invention. The PPO12 comprises 2,6-dimethylphenylene ether units and has an intrinsic viscosity of 0.12xc2x10.02 dl/g as measured in chloroform at 25xc2x0 C. Low molecular weight PPE resins such as PPO12 show reasonably high Tg that equates to high heat performance and have much lower melt viscosity as compared to high molecular weight grades. These two aspects are very important for performance and processibility.
The PPE resins employed to form the crosslinked copolymers of this invention have at least one end cap containing a pair of unsaturated aliphatic carbon atoms, i.e. a carbon-carbon double bond. This end cap increases the reactivity of the PPE polymer so as to facilitate copolymerization with other monomers or copolymers having unsaturated aliphatic carbon atoms such as styrene monomers, acrylonitrile monomers, styrene/acrylonitrile copolymers and combinations thereof, including optionally other polymerizable monomers.
By xe2x80x9ccappedxe2x80x9d, it is meant preferably at least about 80%, more preferably at least about 90%, most preferably at least about 95% of the PPE polymer chains have end caps with a pair of unsaturated aliphatic carbon atoms, preferably vinyl moieties. The PPE polymer chains often have Mannich end groups ((alkyl)2N) formed during the polymerization. These Mannich end groups can be converted to active hydroxy end groups by known techniques to increase the number of end caps per PPE polymer, e.g., by subjecting the PPE resin to elevated temperatures such as, greater than about 150xc2x0 C. preferably greater than about 180xc2x0 C. or higher.
The end caps on the PPE polymer can be provided by reacting the hydroxyl groups of the PPE polymer with a suitable reactive species that provides at least one pair of unsaturated aliphatic carbon atoms. This is carried out by allowing the PPE polymers to react with a suitable capping agent. Suitable capping agents used in the present invention to introduce the aliphatic unsaturation onto the PPE include an unsaturated compound of the general formula (II): 
R1 is an aliphatic, cyclic, or aromatic residue, for example, xe2x80x94CH2xe2x80x94 but may be multiple xe2x80x94CH2xe2x80x94 groups, e.g., n can vary from 1 to about 10 or more, or alternatively, n may equal zero wherein the formula is an acrylic residue. Each of R2, R3, and R4 are independently hydrogen, alkyl (preferably C1-C10 alkyl), or aryl (preferably C6-C10 aryl), and X is a residue of one of the following formulae (III): 
Alternatively, X may be a halogen or may be a residue of the formula (IV): 
R7 is an aliphatic or aromatic residue, for example, xe2x80x94CH2xe2x80x94 but may be multiple xe2x80x94CH2xe2x80x94 groups, e.g., m can vary from 1 to about 10 or more, or alternatively, m may equal zero (if n and m both equal zero, the unsaturated compound is an acrylic anhydride). Each R8, R9, and R10 are independently hydrogen, alkyl, or aryl. In a preferred embodiment, the unsaturated compound is of the formula (V): 
wherein each of n, R1, R2, R3, and R4 are as previously described. In an especially preferred embodiment, the unsaturated compound is of the formula (VI): 
However, included within the scope of the present invention are xe2x80x9cmixedxe2x80x9d or xe2x80x9cunsymmetricalxe2x80x9d anhydrides of formula (V).
The capping agent typically has one or more vinyl groups. The capping agent can be a styrene, a styrene based monomer, a substituted styrene, an acrylic based monomer, acrylonitrile, an acrylonitrile based monomer, an epoxy based monomer, methyl methacrylate, ethyl methacrylate, or other suitable material. The capping agent is preferably an unsaturated anhydride such as methacrylic acid anhydride.
The amount of the above mentioned end capping agents employed is preferably that required to provide at least one end cap for each PPE polymer chain.
As stated herein, the PPE polymer can be capped by the addition of at least one unsaturated anhydride such as methacrylic acid anhydride (MAA), preferably in a solution, to form capped PPE polymer referred to herein as PPE-methacrylic acid anhydride (PPE-MAA). Methacrylic acid anhydride is highly reactive in radical reactions, and is very reactive with styrenic polymers. The PPE-MAA can build into styrenic copolymers via the methacrylate double bond which remains after reaction with the PPE polymer.
The end capping reaction is typically done in the presence of at least one catalyst by conventional methods or by the methods given in the examples which follow. The catalyst is preferably an amine-type catalyst such as DMAP (N,N-dimethylaminopyridine). After the capping step, the PPE resin typically comprises PPE polymer chains having one or two end caps per polymer chain. As previously discussed, it is preferable for at least about 80%, preferably at least about 90%, more preferably at least about 95% or more of the hydroxy groups within the PPE polymer chains to be capped. In an especially preferred embodiment, substantially all of the hydroxyl moieties of the PPE have been capped. Mixtures of endcaps, including mixture of reactive and non-reactive endcaps (endcaps no containing a residual carbon-carbon double bond) may also be used.
Although not wishing to be bound by any theory on the nature or mechanism of the chemical reaction between the PPE and the unsaturated compound of formula (II), it is presumed that the functionalization of the PPE takes place through the hydroxyl groups on the PPE resulting in a PPE containing aliphatic unsaturation comprising the formula (VII): 
Each of Q1, Q2, n, R1, R2, R3, and R4 is as previously defined and j comprises a range of values generally on average between about 10 and 110 depending in large part on the I.V. of the PPE resin.
Additionally, multiple aliphatic unsaturation can also be introduced onto the PPE polymer through incorporation of branching agents and/or coupling agents into the PPE polymer backbone structure such that more than one end of the PPE polymer contains hydroxyl groups for capping. Such branching agents and/or coupling agents are known in the art and include compounds such as, for example, tetramethylhydroquinone and trishydroxyphenol.
A reaction between PPE polymer and capping agent (MAA) is depicted in the figure below 
Ester formation occurs between a phenolic end group of the PPE polymer and the carboxylic group of the methacrylate.
The amount of the above mentioned end capping agents employed is preferably that required to provide, on average, at least one end cap for each PPE polymer chain. The mole ratio of capping agent to hydroxyl group per PPE polymer can range from 0.5:1 to 10:1. These reactions are typically performed at a temperature in the range of 0xc2x0 C. to 100xc2x0 C. in the presence of N,N-dimethylaminopyridine catalyst, (DMAP).
The PPE polymer containing an end cap having at least one pair of unsaturated aliphatic carbon atoms is capable of cross-linking or copolymerizing with other monomers, polymers or copolymers having a pair unsaturated aliphatic carbon atoms by conventional free radical polymerization techniques, typically with an initiator, such as those activated with the application of heat, U.V. radiation or electron beam radiation. An example of a suitable initiator is AIBN, (2, 2xe2x80x2Azo-bis isobutyronitrile). The initiators are typically added at 0.1 wt % or less. Polymerization can also proceed by conventional ionic polymerization, atom transfer polymerization and living free radical polymerization techniques.
The PPE polymers containing end caps as provided herein are copolymerized in conjunction with a) styrene and acrylonitrile monomers or b) styrene/acrylonitrile copolymers or c) a combination of styrene acrylonitrile copolymers, styrene monomers and acrylonitrile monomers to form a crosslinked copolymer. The PPE polymer chains may have two or more end caps to provide multiple reaction sites for forming crosslinks.
The segments of styrene and acrylonitrile units can be derived from styrene and acrylonitrile monomers or styrene/acrylonitrile copolymers or combinations of styrene/acrylonitrile copolymers with styrene and/or acrylonitrile monomers to make the crosslinked copolymer. Styrene/Acrylonitrile copolymers (SAN), also known as poly(styrene-co-acrylonitrile), is a typically simple random copolymers of styrene(S) monomers and acrylonitrile (AN) monomers.
A formula for SAN is shown as formula (VIII): 
wherein n=0-100 and m=0-50.
The styrene/acrylonitrile copolymers (SAN) that can be copolymerized with PPE resin containing the end caps are preferably random copolymers of styrene and acrylonitrile, optionally containing other polymerizable monomers known in the art.
PPE resins containing at least some PPE polymer chains containing two or more end caps are believed to form crosslinked chains between SAN copolymers. With only one end cap, the PPE polymer is integrated with the styrene and acrylonitrile units to form a xe2x80x9ccombxe2x80x9d type structure, with the PPE polymer segments forming the xe2x80x9cteethxe2x80x9d of the comb. Without end caps, the hydroxyl groups on the PPE polymer chains tend to inhibit the polymerization reactions of styrene monomer and styrene/acrylonitrile copolymers. With increasing numbers of PPE polymers having end caps containing carbon-carbon double bonds on both ends, crosslinking between the comb structures increases. The crosslinked copolymers can be derived from PPE resins comprising PPE polymer chains that have two reactive end caps. A solid three-dimensional network structure of inter-connected polymer chains is formed with S, AN and the PPE polymers having 2 or more reactive end caps. This network structure exhibits high heat resistance and solvent resistance.
The PPE-MAA polymers are attached within the three-dimensional structure via the methacrylic double bonds. Logically, cross-linking can be expected to increase with PPE-MAA polymer having methacrylate groups at both chain ends.
To insure successful copolymerization or crosslinking into a network structure, the amount of PPE polymer (loading) which is available for reaction with the SAN is controlled. The amount of capped PPE resin loaded in the reaction medium is preferably 20 wt % or more, based on the total weight of the PPE resin and the polymerizable monomers, e.g., the styrenic monomers and the acrylonitrile monomers. Preferably, the amount of PPE polymer within the reaction medium is 20 to 40 wt %.
At loading levels of 15 wt. % and less, a linear comb structure, rather than a 3-dimensional network structure results. It has also been discovered that at levels above 20 wt. % loading, the PPE-MAA and SAN typically do not polymerize well together when using the typical commercial grades of PPE resin having I.V. greater that about 0.3 as measured in chloroform at 25xc2x0 C. At these loading levels and I.V., the PPE and SAN segments typically form separate polymers in the reaction mix, and settle out separately from each other. However, integrated copolymerization between the PPE and the S and AN segments at loading levels above 20 wt % can be achieved with the use of a low viscosity endcapped PPE polymer as described herein. A low viscosity PPE resin, such as those comprised of PP012-MAA polymers offers a greater number of bonding sites per amount of PPE polymer than higher molecular weight PPE polymer. The PPE resin to be used herein preferably has a viscosity of 0.20 dl/g or less, as measured in chloroform at 25xc2x0 C. more preferably has a viscosity of 0.08 to 0.15 dl/g, and most preferably has a viscosity of about 0.12 dl/g.
Use of the short chain PPE, e.g., PPO12-MAA, results in increased linkage among the PPE segments and polymer segments of styrene, acrylonitrile and both styrene and acrylonitrile, enabling the formation of a three-dimensional network structure. Despite loadings of 20 wt % -40 wt %, the PPE segments can comprise up to 80% or more of the copolymer by weight after copolymerization.
The compositions of this invention can be used for a number of purposes including articles that require high heat resistance and high dielectric constants such as printed circuit boards, electronic components and flame retardant panels.
One of two methods will typically be used for crosslinking or copolymerizing the capped PPE with styrene and acrylonitrile monomers, copolymers of styrene with acrylonitrile, or both. They can be crosslinked or copolymerized using a bulk method or a suspension method. Bulk polymerization comprises performing the reaction without solvent in the presence of a liquid monomer with initiator.
Suspension polymerization is a system in which monomer is suspended as the discontinuous phase of droplets in a continuous phase and polymerized. The continuous phase is usually water, as most monomers are relatively insoluble in water. In suspension polymerization, a catalyst is dissolved in the monomer (styrene/styrene-acrylonitrile), which is dispersed in water. A dispersing agent or surfactant, e.g., poly- (vinylalcohol), is added separately to stabilize the resulting suspension. The chemical properties of products from suspension polymerization may differ from those prepared by bulk polymerization, a factor which should be considered when choosing between the methods. The usual ranges of reaction temperature for the suspension are usually between 40 and 90xc2x0 C. Initiators are added in the range of 0.1 wt % of the monomer or less. The surfactant system helps establish the initial monomer, droplet size distribution, controls droplet coalescence and reduce particle agglomeration. The suspension stabilizer affects particle size and shape as well as the clarity and transparency.
Sample methods for capping the PPE, crosslinking or copolymerizing the capped PPE resin and isolating the copolymer product are illustrated herein.